Since 1998, the Harvard Prevention Research Center (HPRC) has contributed to national recognition that we need replicable, effective prevention strategies as the epidemic of obesity continues. The HPRC works with partners serving youth within focus communities of Boston, Massachusetts and Maine. Using community- based participatory research (CBPR) methods and rigorous evaluation strategies;HPRC has worked effectively with these partners to develop, implement and evaluate groundbreaking work in school, community and health care settings, disseminating these models, materials and curricula locally, nationally and internationally. The HPRC mission is: To work with communities, community agencies, state and local government, and other partners to develop, implement and evaluate methodologies and interventions to improve nutrition and physical activity and reduce obesity and chronic disease risk among children, youth and their families, and to reduce and eliminate disparities in these outcomes. The core research proposal details the implementation of a CBPR intervention and dissemination research project focused on improving nutrition and physical activity environments in out-of-school time settings for children and youth. A 5-year plan for our category-1 funded center builds upon prior success to improve public health practice and policy using CBPR to design, test and disseminate programs at the local, state and national levels, involving community members and researchers as partners. We outline six content-area aims: 1) Community Engagement &Partnerships: Maintain strong, productive partnerships with local community, academic and national partners;2) Infrastructure &Administration: Sustain a multidisciplinary faculty and staff providing strong infrastructure and capacity needed to accomplish our PRC goals;3) Research: Conduct intervention research activities using CBPR and strategies focused on multi-level factors associated with obesity, related health behaviors and disparities;4) Technical Assistance, Training, &Mentoring: Enhancing community and professional capacity by providing opportunities for training, technical assistance and mentoring to researchers, practitioners, students, and community;5) Communication &.Dissemination: Communicate and disseminate research and evaluation findings, products and tools;6) Evaluation: Incorporate evaluation activities within core content areas, documenting activities, outputs and outcomes necessary to assess effectiveness, informing ongoing HPRC activities and National PRC evaluation. RELEVANCE (See instructions): The Harvard Prevention Research Center (HPRC) on Nutrition and Physical Activity proposes to continue its work as a Category 1 Funded Prevention Research Center serving Boston, Massachusetts and Maine from September 2009 to September 2014. We plan to work with communities, community agencies, state and local government, and other partners to develop, implement and evaluate methodologies and interventions to improve nutrition and physical activity and reduce obesity and associated chronic disease risk among children, youth and their families and to reduce and eliminate disparities in these outcomes.